Palladium‐, Platin‐ und Dieisenkomplexe mit Isocyanacetat: Ringschluß, säureinduzierte Ringöffnung, Diprotonierung

Palladium, Platinum, and Diiron Complexes with Isocyanoacetate: Ring Closure, Acid‐Induced Ring Opening, Diprotonation Substitution by isocyanoacetate (CNCH 2 CO 2 − ) of one chloro ligand in trans ‐[MCl 2 (PPh 3 ) 2 ] (M = Pd, Pt) results in the Δ 2 ‐oxazolin‐5‐on‐2‐ato complexes 4a , b , i.e. immediate cyclization occurs in contact with these metal(II) species. In contrast, the open‐chain form of the functional isocyanide is retained in [K(18‐crown‐6][Fe 2 Cp 2 (CNCH 2 CO 2 )(CO) 3 ] ( 16 ) in which it occupies a terminal position. Protonation (alkylation) of the platinum complex 4b proceeds with ring cleavage and formation of isocyano acetic acid 11 (ethyl isocyanoacetate 12 ) stabilized by metal ion coordination. Protonation of 16 requires two equivalents of acid to yield the aminocarbyne‐bridged complex [{ μ ‐C=N(H)CH 2 CO 2 H}Fe 2 Cp 2 (CO) 3 ](BF 4 ) ( 17 ) as the only isolable product. Here isocyanoacetate displays a third kind of reactivity pattern in addition to that at Pd II /Pt II and that at Cr 0 /W 0 where the primary species [M(CO) 5 CNCH 2 CO 2 ] − and [M(CO) 5 CNCH 2 CO 2 H] proved to be the most stable. All of the proposed structures are substantiated by analytical and the usual spectroscopic (IR, NMR{ 1 H, 13 C, 31 P}, FAB‐MS) data, that of 4b also by an X‐ray structure determination which reveals a practically perpendicular arrangement of the coordination and the ring plane, and a long C2‐O bond as the predetermined breaking point of the heterocycle.